Ablation devices are used to ablate tissue inside a patient's body. For example, endometrial ablation devices ablate the endometrial lining of the uterus and some portion of the myometrium of the uterus through application of electrical current applied directly to the tissue. The application of electrical current directly to the tissue increases the temperature of the tissue and causes water in the tissue to boil, thereby generating steam. Areas of the uterine cavity that are not in direct contact with the electrodes that supply the current may also be ablated by contact with the steam generated by the electrical current applied to the tissue. However, there are disadvantages to such devices, such as, for example, the ablation of the tissue may not be uniform due to variations in electrical current density on the surface and near the border of the electrodes. In addition, high current densities at the electrode surface can lead to more ablation of the lining than desired.